Timing of swathing resources
August 23, 2011
Research indicates that the optimum stage to swath is up to an average of 60% seed colour change (SCC) on the main stem. Delaying swathing of any canola variety up to this stage can typically improve yield and quality through increased seed size, reduced green seed and higher oil content, while avoiding economic shattering losses prior to or during swathing. This enables growers with large canola acreages to wait for at least 20 or 30% SCC to swath their first fields and still finish their last fields within the optimum swathing stage.
Seed colour. It is more important than the exterior plant or pod colour when determining the stage of maturity. Visual plant or pod colour will vary among varieties and growing conditions. Some varieties can appear ripe on the outside before the seeds are mature. Hot and/or dry weather at ripening can increase this tendency.
Uneven maturity. Variations in plant emergence, field topography, soil type and soil moisture levels can contribute to a wide range in the maturity of plants within a field. Delay swathing of the least mature areas or plants until there is at least some seed colour change in the lower pods (and firm green seed in the least mature pods), provided this does not put the crop at risk of frost damage or excessive shattering of the ripest plants.
Avoiding green seed. Extreme temperatures (either hot and dry or frost) in fall can lead to rapid desiccation of plant cells which deactivates the enzymes that clear chlorophyll from the seeds. When conditions are hot (30°C or higher) and dry, avoid swathing. Swathing during the cool evening to early morning hours allows plants in the swath to dry down at a slower rate and reduces the chance of downgrading due to green seed. If conditions are cool in late August or early September and frost is forecasted, swath as early as 10% seed colour change to minimize green seed. Protection from frost damage results mainly from dry down of seed in the swath, so sufficient time between swathing and the frost event is needed for this to occur.
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